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Inward rectifier potassium (Kir) current in dopaminergic periglomerular neurons of the mouse olfactory bulb.

Borin M, Fogli Iseppe A, Pignatelli A, Belluzzi O - Front Cell Neurosci (2014)

Bottom Line: The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP.We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors.These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy.

ABSTRACT
Dopaminergic (DA) periglomerular (PG) neurons are critically placed at the entry of the bulbar circuitry, directly in contact with both the terminals of olfactory sensory neurons and the apical dendrites of projection neurons; they are autorhythmic and are the target of numerous terminals releasing a variety of neurotransmitters. Despite the centrality of their position, suggesting a critical role in the sensory processing, their properties -and consequently their function- remain elusive. The current mediated by inward rectifier potassium (Kir) channels in DA-PG cells was recorded by adopting the perforated-patch configuration in thin slices; IKir could be distinguished from the hyperpolarization-activated current (I h ) by showing full activation in <10 ms, no inactivation, suppression by Ba(2+) in a typical voltage-dependent manner (IC50 208 μM) and reversal potential nearly coincident with EK. Ba(2+) (2 mM) induces a large depolarization of DA-PG cells, paralleled by an increase of the input resistance, leading to a block of the spontaneous activity, but the Kir current is not an essential component of the pacemaker machinery. The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP. We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

No MeSH data available.


Related in: MedlinePlus

Barium sensitivity. (A) Percentage inhibition of steady-state Kir current vs. [Ba2+]o. [K+]o = 2.5 mM, 32°C. The data (green dots) were fitted with a logistic function (see text), giving a concentration at half-block (Kd) of 0.21 ± 0.10 mM, and a slope (Hill coefficient) of 0.69 ± 0.23 (n = 5, −120 mV). (B,C): sample tracings obtained in a single cells in response to hyperpolarizing steps from −40 to −120 mV in standard saline plus BL1 and BL2 (B), and in the presence of 1 mM Ba2+(C). (D,E): same experimental conditions and protocol as above; blocking effect of 1 mM Cs+. (F) Voltage dependence of the blocking time constant; the data points were obtained in the presence of 1 mM Ba2+ (yellow dots) or Cs+ (orange dots).
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Figure 2: Barium sensitivity. (A) Percentage inhibition of steady-state Kir current vs. [Ba2+]o. [K+]o = 2.5 mM, 32°C. The data (green dots) were fitted with a logistic function (see text), giving a concentration at half-block (Kd) of 0.21 ± 0.10 mM, and a slope (Hill coefficient) of 0.69 ± 0.23 (n = 5, −120 mV). (B,C): sample tracings obtained in a single cells in response to hyperpolarizing steps from −40 to −120 mV in standard saline plus BL1 and BL2 (B), and in the presence of 1 mM Ba2+(C). (D,E): same experimental conditions and protocol as above; blocking effect of 1 mM Cs+. (F) Voltage dependence of the blocking time constant; the data points were obtained in the presence of 1 mM Ba2+ (yellow dots) or Cs+ (orange dots).

Mentions: The Ba2+ dependent block of IKir was evaluated from the decrease of steady-state current amplitude at −120 mV in the presence of increasing external Ba2+ concentrations. In Figure 2A is represented the percentage of the current inhibition as a function of external Ba2+ concentrations ranging from 1 μM to 10 mM. The data could be interpolated by a logistic equation with the form:


Inward rectifier potassium (Kir) current in dopaminergic periglomerular neurons of the mouse olfactory bulb.

Borin M, Fogli Iseppe A, Pignatelli A, Belluzzi O - Front Cell Neurosci (2014)

Barium sensitivity. (A) Percentage inhibition of steady-state Kir current vs. [Ba2+]o. [K+]o = 2.5 mM, 32°C. The data (green dots) were fitted with a logistic function (see text), giving a concentration at half-block (Kd) of 0.21 ± 0.10 mM, and a slope (Hill coefficient) of 0.69 ± 0.23 (n = 5, −120 mV). (B,C): sample tracings obtained in a single cells in response to hyperpolarizing steps from −40 to −120 mV in standard saline plus BL1 and BL2 (B), and in the presence of 1 mM Ba2+(C). (D,E): same experimental conditions and protocol as above; blocking effect of 1 mM Cs+. (F) Voltage dependence of the blocking time constant; the data points were obtained in the presence of 1 mM Ba2+ (yellow dots) or Cs+ (orange dots).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126183&req=5

Figure 2: Barium sensitivity. (A) Percentage inhibition of steady-state Kir current vs. [Ba2+]o. [K+]o = 2.5 mM, 32°C. The data (green dots) were fitted with a logistic function (see text), giving a concentration at half-block (Kd) of 0.21 ± 0.10 mM, and a slope (Hill coefficient) of 0.69 ± 0.23 (n = 5, −120 mV). (B,C): sample tracings obtained in a single cells in response to hyperpolarizing steps from −40 to −120 mV in standard saline plus BL1 and BL2 (B), and in the presence of 1 mM Ba2+(C). (D,E): same experimental conditions and protocol as above; blocking effect of 1 mM Cs+. (F) Voltage dependence of the blocking time constant; the data points were obtained in the presence of 1 mM Ba2+ (yellow dots) or Cs+ (orange dots).
Mentions: The Ba2+ dependent block of IKir was evaluated from the decrease of steady-state current amplitude at −120 mV in the presence of increasing external Ba2+ concentrations. In Figure 2A is represented the percentage of the current inhibition as a function of external Ba2+ concentrations ranging from 1 μM to 10 mM. The data could be interpolated by a logistic equation with the form:

Bottom Line: The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP.We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors.These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy.

ABSTRACT
Dopaminergic (DA) periglomerular (PG) neurons are critically placed at the entry of the bulbar circuitry, directly in contact with both the terminals of olfactory sensory neurons and the apical dendrites of projection neurons; they are autorhythmic and are the target of numerous terminals releasing a variety of neurotransmitters. Despite the centrality of their position, suggesting a critical role in the sensory processing, their properties -and consequently their function- remain elusive. The current mediated by inward rectifier potassium (Kir) channels in DA-PG cells was recorded by adopting the perforated-patch configuration in thin slices; IKir could be distinguished from the hyperpolarization-activated current (I h ) by showing full activation in <10 ms, no inactivation, suppression by Ba(2+) in a typical voltage-dependent manner (IC50 208 μM) and reversal potential nearly coincident with EK. Ba(2+) (2 mM) induces a large depolarization of DA-PG cells, paralleled by an increase of the input resistance, leading to a block of the spontaneous activity, but the Kir current is not an essential component of the pacemaker machinery. The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP. We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

No MeSH data available.


Related in: MedlinePlus